Antennas of radar sensors which are provided for use in motor vehicles are frequently designed as patch antennas on an HF substrate. This allows a cost-effective structure of the radar sensor. The use of group antennas makes it possible to achieve the desired directional characteristic of the radar sensor in azimuth and/or in elevation without needing a radar lens. Frequently, separate antennas are used for the emission of the radar signal and for the reception of the reflected signal. The desired directional characteristic of the transmitting antenna in azimuth may be achieved in that the microwave power is fed in phase to the multiple antenna elements situated side by side on the substrate. Interference then produces a radar lobe, the main radiation direction of which is oriented at a right angle to the plane of the substrate and covers an azimuth angle range of approximately −45° to approximately +45°. On the receive side, multiple antenna elements or patches also situated side by side are used, which, however, are associated with different receive channels, making it possible to infer the azimuth angle of the object based on the phase differences between the signals received by the different antenna elements.
In particular, the present invention relates to a rear area radar sensor system for motor vehicles, for example, in an LCA system (Lane Change Aid), which supports the driver when changing lanes by warning of vehicles approaching on the same lane or the passing lane from behind. In this case, the radar sensor system in the rearward direction must have a large range, so that even fast vehicles may be detected in time, and on the other hand, it should be able to locate vehicles which are situated at a short distance or nearly abreast on the passing lane and are thus situated in the driver's blind spot.